stephkhaira wrote:6 machines work at the same constant rate and it takes them 12 days to complete 1 job. If the job must be done in 8 days, how many machines should be added?
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[spoiler]ans: 3[/spoiler]
Let the rate for each machine = 1 unit per day.
Rate for 6 machines = 6 units per day.
In 12 days, the amount of work produced = r*t = 6*12 = 72 units.
To produce 72 units in 8 days, the required amount of work per day = w/t = 72/8 = 9 units per day.
To increase the rate from 6 units per day to 9 units per day, 3 more machines are needed.
The correct answer is
B.
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